Hi Katie, My wife and I have tried the last 3 years to summit as a day hike and didn't make it either. We did get closer each year and last year we were less than a half mile from the top when I gave up. I agree with the other poster to take food you really like and probably avoid anything dry. My appetite definitely was affected by altitude or exhaustion or both. Most hikes trail mix and similar food is all I need but for Whitney I would also recommend those chewy energy bars. A hiker last year realized I was struggling and gave me some of his with caffeine. Without that I may still be trying to get back to the trailhead. Good luck!
